1. Field of the Invention
This invention relates to bearing lubrication systems and, in particular, to lubrication systems having a pressurized oil reservoir and an emergency gas system for backup flow capability.
2. Description of Prior Art
As is well known, a large turbine apparatus converts high-pressure, high temperature energy carried by motive steam into rotational mechanical energy. This transformation is accomplished by permitting the steam to expand through alternating arrays of stationary and rotating blading disposed, respectively, within the turbine casing and on a rotor member extending centrally and axially therethrough. At each axial end of the rotor at a point thereon exterior to the casing is provided a suitable bearing to rotatably support the rotor member. In order to assure that the bearings optimumly perform this function, it is of primary importance that they be supplied with a suitable lubricating fluid. For this purpose, the prior art has disposed elaborate bearing lubricating fluid systems to supply the necessary lubricant to the bearings.
At present, steam turbine lubricating systems utilize an oil pump mounted on the turbine rotor shaft as a device to provide lubricating oil under pressure to the turbine bearings. This shaft-mounted oil pump uses the kinetic energy of the rotor to provide an energy source independent of other interruptible power sources to convey fluid to the bearings. The shaft-mounted main oil pump provides motive oil to an oil ejector, or hydraulic turbine, which is located within a lubricating fluid reservoir. The discharge of the ejector supplies lubricating fluid under pressure to an oil cooler and then to the turbine bearings. A portion of the pressurized fluid at the discharge of the ejector is also supplied to the shaft-mounted pump suction to prime the shaft-mounted pump, i.e., to maintain a supply of fluid thereto.
After serving its lubricating purpose within the bearing member, oil returns to the reservoir by gravity through a suitably disposed oil strainer. The reservoir itself is located a significant distance beneath the centerline of the turbine apparatus which it serves. All of the oil supply lines emanating from the reservoir to the bearings are surrounded by a guard pipe to insure that any leak developed within the fluid lines will drain to the oil reservoir. As a concomitant to this safety requirement, it is apparent that the reservoir itself must be of sufficient size to hold all the run-back of oil of the entire system. Motor-driven pumps are mounted on the reservoir and provide oil to the turbine bearing during those periods when the rotor is moving up to or coming down from rated speed.
Any oil lubricating system, the above-described being typical of a prior art embodiment, must meet the three so-called reliability constraints. To meet these reliability constraints, a lubricating system must, first, provide oil to the bearing with minimal possibility of any interruption of oil supply system pressurization; second, provide oil at a temperature cool enough to be utilized by the bearings; and, third, provide oil to the bearings that is not contaminated by foreign matter. In addition to the reliability constraints just outlined, it is desirable that a lubricating system be efficient so as not to overly detract from the efficiency of the entire power plant. With these requirements in mind, it is apparent that the prior art systems, although meeting the reliability requirements, do so with a minimum regard for the overall efficiency of the lubricating system.
For example, although a shaft-mounted pump is reliable in the sense that flow to the bearings is maintained regardless of pump electric or steam power interruptions, since the fluid reservoir is located a significant distance below the turbine centerline, considerable power from the shaft-mounted pump is required in order to provide the necessary motive power to lift the lubricating fluid from the reservoir to the turbine bearings and also to the shaft-mounted pump suction. On a typical unit, for example, such a turbine shaft-mounted pump requires 800 horsepower in order to provide motive oil for the lubrication functions. As a further disadvantage, if the system utilizes an ejector to pressurize the oil flowing to the bearings, a limited discharge pressure is available due to the very nature of the ejector apparatus. Therefore, there is a limited range of distances that the reservoir may be located from the turbine, thus reducing overall power plant flexibility. Further, the motor driven pumps mounted on the reservoir may themselves require 75 to 100 horsepower to provide fluid to the bearings when they are called upon to do so.
A still further disadvantage in the prior art systems is the high temperature at which fluid is stored in the reservoir. The prior art maintains fluid in the reservoir at the drain temperature of approximately 150.degree. F. In the event of loss of cooling water to the oil coolers located downstream of the reservoir, there is danger of damage to the bearings due to the introduction thereinto of hot oil, in contravention of the second reliability requirement discussed above. Yet another limitation in the efficacy of prior art lubrication systems is the inability to effectively eliminate foreign contaminants from the fluid before the fluid leaves the reservoir. Also, the physical size of the conduits required by prior art systems occupies a greater portion of power plant area than is economical, thus directly increasing the cost of these facilities.
It is apparent that an improved lubricating fluid system for the bearing of a turbine apparatus which eliminates these aforementioned problems of the prior art is required.